Most of the research and development efforts in the field of lighting devices are known to be aimed at maximizing lighting efficiency.
This need is particularly felt especially for outdoor lighting devices, where the light beam should be optimally directed, because any dispersed light beams are totally lost, unlike indoor lighting, where some reflection is provided by surrounding walls.
Particularly significant examples are street lighting applications, where the target to be lighted is particularly small, whereby the light beams emitted from light sources must be accurately directed.
A light source is known to emit light beams substantially in all directions. This means that a considerable part of these beams cannot light the target and is thus lost.
In this respect, the prior art provides lighting devices in which the light source is surrounded by reflecting surfaces on all the sides that do not face the target. These surfaces may have various shapes, but are all aimed at optimizing the collection of light beams that would otherwise be lost and reflecting them towards the target.
This will afford a considerably improved luminous efficacy, but it does not provide relevant results due to other drawbacks.
First, since the device is generally placed at a considerable distance from the target, many light beams are anyway dispersed.
Furthermore, the light sources that are generally used, i.e. incandescent, halogen or fluorescent sources have such a size as to act themselves as a screen for most of the light beams, which are thus irreparably lost.
In an attempt to improve these results, lighting devices are known that use LEDs. These can be generally approximated to point-like light sources, and hence at least partially obviate the problem of the screen effect of the source. Nevertheless, they increase the problem of substantially even distribution of light emission in all directions, which decreases their luminous efficacy on the target.
WO20081103379 discloses a LED lighting system. However, nowhere in this prior art there is mentioned the FWHM of its luminous spectrum or its reflection by at least one of the reflecting surfaces and projection towards a target.
Moreover, the outwardly directed aperture is not facing toward the target but toward a remote reflector.
Lighting devices are also known which use refractive or Fresnel lenses to improve the directivity of the emitted light beam. However, little improvements are obtained also in this case.